Display having structures to regulate orientation of liquid crystal molecules

ABSTRACT

A liquid crystal display includes a first substrate and a second substrate, a liquid crystal between the first and second substrates, and first and second structures provided on the first and second substrates to regulate orientation of liquid crystal molecules in the liquid crystal layer.

This is a continuation of U.S. Ser. No. 11/240,340, filed Sep. 30, 2005now U.S. Pat. No. 7,535,532, which claims foreign priority under 35U.S.C. §119 of Taiwan Application 93129719, filed Sep. 30, 2004, bothhereby incorporated by reference.

TECHNICAL FIELD

This invention relates generally to liquid crystal displays (LCDs).

BACKGROUND

A liquid crystal display (LCD) typically includes a unit having twoglass substrates (or other types of substrates) that face each other,with a liquid crystal layer sandwiched between the substrates. An LCD ina vertically aligned (VA) mode uses negative liquid crystal material andvertically aligned film. When not supplied with a voltage, the liquidcrystal molecules in the liquid crystal layer are arranged in a verticaldirection (with respect to the main surfaces of the substrates) and theVA LCD cannot be penetrated by an incident light, resulting in a darkdisplay. When supplied with a preset voltage, liquid crystal moleculesare arranged in a horizontal direction and the VA LCD can be penetratedby an incident light, resulting in a white display.

However, when viewed at an angle not perpendicular to the display, auser may perceive a contrast reduction or contrast reversal problem witha VA LCD. This is the result of interaction of the light with the liquidcrystal molecules within the LCD. When traveling through the LCD in adirection that is not at a right angle of incidence, the light interactswith the liquid crystal molecules in a way different from that when thelight travels through the LCD in a direction at a right angle ofincidence. Therefore, the contrast between the state when the lightpenetrates (white) and the state when the light does not (black) willdrop significantly when the light is not at a right angle of incidence.This results in unsatisfactory performance of VA LCDs in manyapplications (e.g., flat television displays and large computerdisplays).

A larger viewing angle can be provided by an LCD in MVA (multi-domainvertical alignment) mode. In an MVA LCD, improvement in viewing angle isachieved by setting the orientations of the liquid crystal moleculeswithin each pixel of the display to a plurality of different directions.In some conventional MVA LCDs, a multi-domain regulation is provided toimprove the display's performance at various viewing angles. Typically,this multi-domain regulation is achieved by providing a plurality ofslits in the pixel electrode of the thin film transistor substrate and aplurality of protrusions at the common electrode of the color filtersubstrate, where the protrusions and slits are arranged in analternating fashion. The aligned orientation of the liquid crystalmolecules depends on the fringe field produced by the pattern of theprotrusions and slits.

To drive an LCD, a voltage is applied to cause the corresponding liquidcrystal molecules within each pixel to switch. The switching of themolecules will change the light transmittance of each pixel. In responseto switching of the liquid crystal molecules, the LCD will providedifferent brightness. For most LCDs, the higher the applied voltage, thequicker the response if the initial voltage is kept constant. However,this quicker response time at higher applied voltages may not be truewith certain LCDs, such as LCDs in the patterned vertical alignment(PVA) mode and MVA mode. In such LCDs, under certain circumstances, theLCDs may respond slower when a higher voltage is applied.

FIG. 11A shows an arrangement of protrusions and slits in the pixel areaof a conventional MVA LCD. FIG. 11B shows a cross-section along line A-Ain FIG. 11A. As depicted in FIG. 11A, a pixel area 400 of the LCD isdefined generally near the intersection of a gate line 402 and a dataline 404. The pixel area 400 has a thin film transistor (TFT) 406, whichis electrically connected to the gate line 402 and the data line 404.The pixel area 400 also contains a pixel electrode 419 that is connectedto the TFT 406.

As depicted in FIG. 11B (cross section along line A-A′ in FIG. 11A),protrusions 410 and slits 412, provided in the pixel area 400, areformed in a color filter substrate 414 and a TFT substrate 416,respectively. The arrangement of protrusions 410 and slits 412 depictedin FIGS. 11A-11B causes the liquid crystal molecules and the penetrationaxis of the upper and lower polarizers (not shown) to be oriented suchthat the liquid crystal molecules and the penetration axis of the upperand lower polarizers form an angle of 45°, which enables the MVA LCD toprovide maximum gray scale brightness due to light traveling through theMVA LCD. However, when the orientation of the liquid crystal moleculesand the penetration axis of the upper and lower polarizers (not shown)fail to form an angle of 45° under regulation of protrusion 410 and slit412, which may occur when a gap between protrusions and slits becomestoo large, disclination of the liquid crystal molecules occurs. In aliquid crystal cell, disclination refers to the orientation of theliquid crystal molecules changing uncontinuously at a point or a line.Disclination of liquid crystal molecules results in the MVA LCD notbeing able to provide maximum gray scale brightness.

FIGS. 12A-E simulate the switching of the liquid crystal molecules inarea 419 of FIG. 11A. The switching, which is observed within the sametime duration, is caused by the fringe field produced by the pattern ofthe protrusions and slits when different voltages are applied. Thetransverse axis and vertical axis in FIGS. 12A-E correspond todirections A-A′ and A-B of FIG. 11A, respectively. As shown in FIGS. 12Aand 12B, when the voltage applied is 5V and 5.5V. respectively, theliquid crystal molecules in area 418 are arranged by the fringe field ina normal pattern. However, as shown in FIGS. 12C-E, when the voltageapplied rises to 5.75V, 6.0V, and 6.5V, liquid crystal molecules inseveral regions (e.g., 420 a and 420 b) of the area 418 will not bearranged by the fringe field, and as a result, disclination occurs inregions 420 a and 420 b. Disclination is worse in regions 420 a and 420b of FIG. 12E, which shows the result of an applied voltage of 6.5V.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention are described with reference to thefollowing figures:

FIGS. 1-7 depict pixel regions of MVA (multi-domain vertical alignment)liquid crystal displays (LCDs) according to several embodiments of theinvention;

FIG. 8 is a perspective sectional view of an MVA LCD according to anembodiment;

FIG. 9A is a graph of a driving voltage of a pixel as a function of timeaccording to a multi-step driving technique according to an embodiment;

FIG. 9B is a graph of a brightness of the pixel as a function of time inresponse to the driving voltage of FIG. 9A;

FIG. 10 is a block diagram of a display module and a data compensationdevice, according to an embodiment;

FIGS. 11A-11B illustrate an arrangement of a portion of a conventionalMVA LCD; and

FIGS. 12A-12E illustrate simulated switching of liquid crystal moleculesin the conventional MVA LCD of FIGS. 11A-11B.

DETAILED DESCRIPTION

In accordance with some embodiments, an MVA (multi-domain verticalalignment) LCD (liquid crystal display) with a high aperture ratio isprovided. Such an MVA LCD generally includes first and second substratesprocessed for vertical alignment, a liquid crystal layer sandwichedbetween the first and second substrates, and an arrangement ofprotrusions and slit patterns provided on the first and secondsubstrates. A “protrusion” is a structure that projects outwardly awayfrom a surface of another structure, such as a common electrode, pixelelectrode, or other structure. A “slit pattern” includes a pattern ofslits (which are basically openings formed in a surface). Protrusionsand slits are structures that regulate orientations of liquid crystalmolecules in the liquid crystal layer.

The liquid crystal molecules in the liquid crystal layer are alignedgenerally perpendicularly to the principal surface of the firstsubstrate when no substantial electric field is applied to the liquidcrystal layer. The protrusions and slit patterns regulate theorientation of the liquid crystal molecules to obliquely align theliquid crystal molecules in a plurality of directions when a voltage isapplied, which provides improved viewing angle of the MVA LCD. In otherwords, the liquid crystal molecules are inclined in a plurality ofdifferent directions when a voltage is applied. The protrusions and slitpatterns are generally parallel to each other and are arranged in analternating fashion.

In some embodiments, a plurality of protrusions are arranged in arrayson the first substrate, and a plurality of slit patterns are arranged inarrays at pixel electrodes on the second substrate. Alternatively, theslit patterns can be provided at a common electrode on the firstsubstrate, while the protrusions are provided on the second substrate.In yet another arrangement, both protrusions and slit patterns can beprovided on each of the first and second substrates. In furtherembodiments, protrusions can be formed on both the first and secondsubstrates, or slit patterns can be formed on both the first and secondsubstrates.

Optionally, in some embodiments, an improved pixel voltage drivingtechnique is employed, such as that described in U.S. Ser. No.11/198,141, entitled “Method and Apparatus for Driving a Pixel Signal,”filed Aug. 5, 2005, which is hereby incorporated by reference. Theimproved pixel voltage driving technique involves multi-step voltageapplication, in which a pixel signal is provided (on a data line) to thepixel selected by a scan line (or gate line), where the pixel signal isdriven from an initial voltage to an intermediate voltage (larger thanthe initial voltage), then after a time interval, from the intermediatevoltage to a target voltage (larger than the intermediate voltage). Themulti-step driving technique causes an initial voltage of the pixelsignal to rise to an intermediate voltage by adding a first bias voltagesmaller than the critical bias voltage (also referred to as a reversedbias voltage) in frame time t1. Next, in frame time t2, a second biasvoltage is added to the intermediate voltage to further increase thedriving voltage from the intermediate voltage up to the target voltageof the pixel signal. By using this driving method, the response time ofpixels is improved by using the multi-step voltage applicationtechnique.

According to optical-electronic characteristics of liquid crystalmolecules, a pixel has a reversed bias voltage v_(cg1) corresponding toan initial voltage via. When an instant variation (a bias voltage) of adriving voltage is larger than the reversed bias voltage v_(cg1), liquidcrystal molecules of the pixel may switch abnormally, which may lead toincreased response times of the pixel.

To avoid this undesirable situation, as shown in FIG. 9A, according toan embodiment of the multi-step driving technique, the pixel signal hasan initial voltage v_(g1) during a current frame period t_(fo). Theinitial voltage v_(g1) may be the target voltage for the pixel in aprevious frame period t_(fp). The multi-step driving technique accordingto some embodiments of the invention supplies bias voltages in pluralsteps from the initial voltage v_(g1) to the target voltage V_(g3) toavoid a voltage step greater than the reversed bias voltage v_(cg1). Asdepicted in FIG. 9A, this means that a voltage step from the initialvoltage v_(g1) to a voltage greater than the reversed voltageV_(reversed) (the reversed voltage V_(reversed) is a voltage of theinitial v_(g1) voltage plus the reversed bias voltage v_(cg1) of thepixel) is avoided. At a time t_(m), which is at or near the beginning ofthe current frame period t_(fo), a first bias voltage v_(mg1) issupplied Application of the first bias voltage v_(mg1) causes a voltagestep from the initial voltage to the higher intermediate voltage v_(m),where V_(mg1)<v_(cg1). Then, at a time t_(g3), which occurs a timeinterval after t_(m), a second bias voltage v_(g3m) is supplied, whichcauses the driving voltage to increase from the intermediate voltagev_(m) to the higher target voltage v_(g3). The intermediate voltagesupplied to the pixel is maintained constant at the intermediate voltagev_(m) for a time interval between t_(m) and t_(g3).

Note that the time interval t_(g3)-t_(m) of the multi-step drivingtechnique (time interval during which the applied voltage steps from theinitial voltage to the intermediate voltage than to the target voltage)may in some embodiments be less than the current frame period (t_(fo)).A “frame” represents a complete image from a series of images. A “frameperiod” contains an active period and a blanking period, where theactive period is the time period to drive all pixels of an LCD panel,and the blanking period is used to match the period for blankingperformed in CRT (cathode ray tube) monitors.

As noted above, different initial voltages correspond to differentreversed bias voltages. Thus, after the voltage has been driven to theintermediate voltage v_(m), it should be noted that the intermediatevoltage itself is associated with its respective reversed bias voltagev_(cm) (not shown). Therefore, the second bias voltage v_(g3m) appliedat time t_(g3) should be smaller than this reversed bias voltage v_(cm).The issue of abnormal switching of liquid crystal molecules and slowerresponse time of the pixel are usually more pronounced at lower initialvoltages, so it is usually more productive to reduce the magnitude ofthe first bias voltage v_(mg1) than the subsequent applied bias voltageafter elevation of the applied voltage to the intermediate voltage.

FIG. 9B is a diagram showing changes of pixel luminance in relation totime in response to the voltages applied in FIG. 9A. In response to thevoltage being raised to the intermediate voltage v_(m) that is less thanthe bias voltage in the interval between time t_(m) and the time t_(g3),the luminance of the pixel is raised from an initial luminance b_(g1) toan intermediate luminance b_(m). In response to the subsequent raisingof voltage from v_(m) to V_(g3), the luminance is raised continuously toa target luminance b_(g3). Because the first bias voltage v_(mg1)supplied by the multi-step driving technique is less than the reversedbias voltage v_(cg1), the liquid crystal molecules within the pixel canrotate normally (in other words, the liquid crystal molecules are notcaused to rotate in the wrong directions), and the luminance of thepixel can be raised to the predetermined target luminance b_(g3) withimproved response time.

FIG. 10 illustrates an example display module 500 that includes adisplay driving device 502 for driving an LCD panel 504. The displaydriving device 502 includes a data driver module 506 for driving datalines (also referred to as source lines or column lines) of the LCDpanel 504. The display driving device 502 also includes a scan drivermodule 508 for driving scan lines (also referred to as row lines) of theLCD panel 504.

A timing controller 510 in the display driving device 502 receives imagedata, and in response to the image data, supplies signals correspondingto the image data to the data driver module 506. The data driver module506 in turn drives signals on data lines to appropriate voltage levelsaccording to the signals corresponding to the image data, The timing ofdrivers in the data driver module 506 and scan driver module 508 arecontrolled by the timing controller 510.

In accordance with some embodiments of the invention, the image datareceived by the display driving device 502 includes compensation imagedata generated by a data compensation device 512. The compensation imagedata received by the display driving device 502 allows for theapplication of stepped voltage levels (multi-step voltage application ormulti-step driving technique) within a frame period to selected ones ofpixels in the LCD panel 504 under certain conditions.

A voltage (of a pixel signal) provided on a data line by the data drivermodule 506 is communicated through a TFT of the LCD panel for a selectedpixel. The TFT is turned on by activating a scan line by the scan drivermodule 508. The voltage applied on the data line, when communicatedthrough the TFT to a pixel, causes rotation of corresponding liquidcrystal molecules.

Using the multi-step driving technique allows the gap betweenprotrusions and slit patterns in an LCD according to some embodiments tobe increased in size, such as to a distance that is greater than orequal to 25 μm (micrometers) at least at some portions between any pairof adjacent protrusion and slit pattern. If the multi-step drivingtechnique is used, gap size between the protrusion and slit pattern canbe increased without resulting in the problem of disclination of liquidcrystal molecules.

In some embodiments, each slit pattern can have a plurality of jaggednotches. When slit patterns with jagged notches are used in conjunctionwith the multi-step driving technique for pixel signals, the gap betweena protrusion and a slit pattern that has jagged notches can be furtherincreased in size to range between 30 μm and 50 μm, at least betweensome portions of the protrusion and slit pattern, without the problem ofdisclination of liquid crystal molecules.

By providing a larger gap between protrusions and slit patterns, an MVALCD can be configured to have a reduced density of the protrusions andslit patterns. This will effectively increase the aperture ratio (theratio of light transmissible area) and improve the brightness of theLCD.

In some embodiments, each protrusion has a plurality of branches, whichare spaced apart from and located opposite respective edge portions of apixel electrode. Each pixel electrode is divided into a plurality ofpartial electrodes by slit patterns and neighboring or adjacent partialelectrodes are connected to each other by a joint connector. Each jointconnector has a first part and a second part. The first part extends ina direction that is generally perpendicular to the direction of theprotrusions, and the second part extends in a direction that isgenerally parallel to the data lines. In some embodiments, the secondpart of each joint connector completely overlaps the branch of anadjacent protrusion.

According to an example embodiment, the LCD is a thin film transistor(TFT) LCD. As shown in FIG. 8, the TFT LCD includes a first substrate102 which may be provided with a light shielding array, e.g., a blackmatrix (BM) (not shown in FIG. 8), a plurality of color filters 102 aand a common electrode 102 b. The first substrate 102 is also referredto as a color filter substrate.

The TFT LCD also includes a second substrate 104, which includes TFTs,data lines, scan lines, and other structures that are part of pixelregions on the second substrate 104. The second substrate 104 is alsoreferred to as a TFT substrate. A spacer (not shown) is provided betweenthe first substrate 102 and the second substrate 104 to define a gapbetween the two substrates. A liquid crystal layer 103 is providedbetween the substrates 102 and 104.

FIG. 1 shows a portion of an LCD according to an embodiment which isprovided on the TFT substrate 104 (FIG. 8). The TFT substrate 104includes a plurality of gate lines (or scan lines) 106 (which aregenerally parallel to each other), a plurality of data lines 108 (whichare generally parallel to each other and perpendicular to gate lines106), and a plurality of TFTs 109 and pixel electrodes 120. Each TFT 109has a gate electrode electrically connected to a gate line 106, a sourceelectrode electrically connected to a data line 108, and a drainelectrode electrically connected to a pixel electrode 120. As used here,the term “source” and “drain” of a TFT are interchangeable.

When a scanning signal is activated on a respective gate line 106, theTFT 109 is turned on to provide the data signal (on a respective dataline 108) through the TFT 109 to the pixel electrode 120. The datasignal on the data line 108 that is provided to through the TFT 109 tothe pixel electrode is also referred to as a pixel signal. The TFTs 109and pixel electrodes 120 are generally arranged in a matrix atrespective pixel regions proximate intersections of respective gatelines 106 and data lines 108.

Each pixel electrode 120 is provided in the pixel area defined by twoadjacent gate lines 106 and two adjacent data lines 108. In the LCDaccording to an embodiment a plurality of protrusions 130 are arrangedin arrays on the color filter substrate 102. Also, a plurality of slitpatterns 140 are arranged in arrays at the pixel electrodes 120 on theTFT substrate.

The protrusions 130 and slit patterns 140 are generally parallel to eachother and are arranged in alternating fashion. Each protrusion and slitpattern extends generally diagonally across a pixel electrode. The pixelregion depicted in FIG. 1 is separated into two halves by dashed line121. In the upper half, the protrusions and slit patterns extendgenerally diagonally along a first direction, while in the lower half,the protrusions and slit patterns extend generally along a seconddirection that is generally perpendicular to the first direction.

The alternating arrangement of the protrusions and slit patterns meansthat there is a slit pattern interposed between two protrusions, andthere is a protrusion between two slit patterns.

As depicted in FIG. 1, each slit pattern 140 is provided with aplurality of jagged notches 140 a (to achieve a general teeth profile).The gap between a side of a protrusion 130 and a side of an adjacentslit pattern 140 is identified as c. The gap c is equal to the smallestdepth a of the jagged notches 140 a plus the gap b between the base ofnotches 140 a with the smallest depth of protrusions 130. It isdesirable for the gap c to be increased to reduce density of theprotrusions and slit patterns in the LCD for increased aperture ratio ofthe LCD.

When the slit patterns 140 are not provided with the jagged notches 140a, and a conventional driving technique is used for the LCD, the gap (c)between the protrusions 130 and the slits 140 would have to be less than25 μm (in some implementations) to avoid disclination of liquid crystalmolecules. If the 25-μm gap is not provided, the liquid crystalmolecules located in the area sandwiched between the adjacent protrusionand slit pattern are prone to disclination due to excessive transientvariation of the driving voltage (bias voltage), leading to longerresponse time of pixels or image retention problem of displays.

However, if the multi-step driving technique of U.S. Ser. No.11/198,141, is used, the disclination of liquid crystal molecules isreduced so that the gap c between said protrusions 130 and said slitpatterns 140 does not have to be set below 25 μm. As a result, the gap cmay be greater than or equal to 25 μm (at least between some portions ofneighboring protrusion and slit pattern) without causing thedisclination problem with the liquid crystal molecules.

Providing the slit patterns 140 with jagged notches 140 a also allowsfor increasing the gap c. By using the jagged notches 140 a inconjunction with using a conventional pixel signal driving technique,the response time is shortened (as compared to the response time whenslit patterns 140 without the jagged notches 140 a are used). As aresult, the gap c between the protrusions 130 and the slit patterns 140can be set be smaller than 30 μm to avoid disclination of the liquidcrystal molecules.

If the multi-step driving technique is used, the gap c between theprotrusions and the slits with jagged notches can be increased furtherto range between 30 μm and 50 μm without the disclination problem withthe liquid crystal molecules.

Additionally, the transmittance of the LCD is related to the gap dbetween the jagged notches 140 a and the width e (see FIG. 2). Oneexample of this relation is depicted in Table 1 (gap c is set to 35 μmand the smallest depth a is set to 14 μm).

TABLE 1 d (μm) e (μm) Transmittance d/(d + e) (d + e) 4.5 2.5 Excellent64.3% 7.0 4 3 Excellent 57.1% 7.0 3.75 3.25 Excellent 53.6% 7.0 4 3.5Good 53.3% 7.5 4 4 Good 50.0% 8.0 4.5 4 Good 52.9% 8.5 5 4 Good 55.6%9.0

It can be seen from Table 1 that the design of the jagged notches 140 ais such that the gap d and the width e add up to 7˜9 μm (in someimplementations) in order to obtain good transmittance.

Table 2 below illustrates how the gap d between the jagged notches 140 aand the width e (see FIG. 2) relate to the response time achieved byusing a conventional pixel signal driving technique, with the gap c setto 35 μm and the smallest depth a is set to 14 μm, in the depictedexample.

TABLE 2 d (μm) e (μm) Response time 4.5 2.5 Good 4 3 Excellent 3.75 3.25Excellent 4 3.5 Excellent 4 4 Excellent 4.5 4 Excellent 5 4 Poor

Table 2 shows that the gap d between the jagged notches 140 a should beno greater than 4.5 μm and the width e of the jagged notches 140 ashould be no less than 3 μm, in one implementation, in order to obtain agood response time.

In one example implementation, for improved transmittance and responsetime, the jagged notches 140 a are arranged so that the gap d betweenthe notches and the width e should add up to 7˜8.5 μm.

In the LCD illustrated in FIG. 1, each protrusion 130 has a plurality ofbranches 130 a, which are provided at locations directly oppositerespective edges of the pixel electrode 120. In a region near a branch130 a, the long axis of the liquid crystal molecules will be alignedperpendicularly to the branch 130 a. For liquid crystal molecules thatare further away from a branch 130 a, the long axis of the such liquidcrystal molecules will be aligned perpendicularly to the adjacent slitpattern 140. To reduce variation of alignments of liquid crystalmolecules in regions where a slit pattern 140 borders a branch 130 a(close to an edge portion of the pixel electrode 120), such as to keepthe variation of the alignments of liquid crystal molecules to no morethan 45°, the angle formed by the branch 130 a and the slits 140 (angle141 in FIG. 1) is set to less than or equal to 45°, in one exampleembodiment. This will effectively reduce the chance of disclinationoccurring in the regions where slit patterns 140 border branches 130 a.

However, the protrusions 130 and the pixel electrode 120 are separatelyformed on different substrates and misalignment between differentsubstrates often causes the branch 130 a not to be accurately placedopposite an edge portion of the pixel electrode 120 so that a darkenedarea appears at the area where slit patterns 140 border the pixelelectrode as a result of disclination of the liquid crystal molecules.

As shown in FIGS. 1 and 4, the pixel electrode 120 is divided by theslits 140 into four partial electrodes, e.g., 120A, 120B, 120C, and120D. Adjacent partial electrodes are connected to each other via atleast a joint connector 122. Each joint connector 122 has a first part122 a and a second part 122 b (see FIG. 4). The first part 122 a extendsin a direction that is generally perpendicular to the direction of theprotrusions 130. The second part 122 b extends in a direction that isgenerally parallel to the data lines 108. In this embodiment, the secondpart 122 b of each joint connector 122 does not completely overlap thebranch 130 a of the protrusion 130 (i.e., the second part 122 b is notperpendicularly projected onto the substrate plane in exactly the samearea as the branch 130 a). The area in which the second part 122 b doesnot overlap the branch 130 a will appear darkened. In the darkened area,the liquid crystal molecules change their orientation very slowly when avoltage is applied. This reduces the contrast and response time,resulting in deteriorated display quality. If the two substrates aremisaligned, causing the second part 122 b not to overlap the branch 130a, the non-overlapped area will appear darkened.

To address this issue, FIG. 5 shows that the second part 122 b of eachjoint connector 122 completely overlaps the branch 130 a of theprotrusion 130 (i.e., the second part 122 b is perpendicularly projectedonto the substrate plane in exactly the same area as the branch 130 a).This embodiment effectively reduces the above mentioned darkened area.Even when there is misalignment of the two substrates in the up-downdirection as shown in FIG. 5, this design can effectively reduce thedarkened area.

FIG. 3 shows a portion of an MVA LCD according to another embodiment. Inthis embodiment, each pixel area of the LCD is provided with a generallyH-shaped storage capacitance electrode 150 (a capacitance conductorline) that has two side parts (or conductor lines) 150 a connected toeach other via a central part 150 b. As shown in FIG. 3, the two sideparts 150 a are provided in the pixel area at locations adjacent datalines 108. In contrast to the capacitance electrode of a conventionalLCD which is generally designed to have only the central part 150 b, thecapacitance electrode 150 according to the embodiment of FIG. 3 has thetwo side parts 150 a that can provide an additional storage capacitancewhere it overlaps the pixel electrode 120.

The capacitance electrode 150 generally is created along with gate line106 and gate electrode by patterning a gate metal layer. The capacitanceelectrode 150 and gate line 106 are shown in FIG. 3 as a gray patternfor easier understanding. The gate metal layer is generally formed of anelectrically conductive but opaque metal, such as aluminum, chromium,tantalum, or molybdenum. The two side parts 150 a of the capacitanceelectrode 150 may be used as an ancillary light shielding layer toshield light leakage.

FIG. 6 shows a portion of an MVA LCD according to yet anotherembodiment. In this embodiment, a plurality of protrusions 230 arearranged in arrays on the color filter substrate. A plurality of slitpatterns 240 are arranged in arrays at the pixel electrodes 220. Theprotrusions 230 and slit patterns 240 are arranged in an alternatingfashion and the slit pattern 240 located between two adjacentprotrusions 230 has a general serpentine-shaped profile. In the upperhalf of the pixel area above dashed line 256, the generalserpentine-shaped profile of the slit pattern 240 is defined generallyby edge segment 250, edge segment 252, and an intermediate segment 254interconnecting the edge segments 250, 252. In the lower half of thepixel area below dashed line 256, the general serpentine-shaped profileof the slit pattern 240 between protrusions 230 is defined generally beedge segment 258, edge segment 260, and intermediate segment 262interconnecting the edge segments 258, 260.

As shown in FIG. 6, the pixel electrode 220 is divided by the slitpatterns 240 into three partial electrodes, e.g., 220A, 220B, and 220C.Adjacent partial electrodes are connected to each other via at least oneconnector joint 222. The partial electrodes 220A, 220B, and 220C eachhas a plurality of projections 224, which extend in a direction that isperpendicular to that of the protrusions 230. Note that the projectionsof each partial electrode forms the notches of the respective slitpattern. The projections 224 of the partial electrodes depicted in FIG.6 are longer than the projections of partial electrodes depicted inFIG. 1. In the FIG. 6 embodiment, the protrusions 230 are not providedwith any branches that are parallel to the data lines, which would havebeen located opposite an edge portion of the pixel electrode adjacent tothe data lines. The projections 224 are extended because of the removalof the branches in these locations. By eliminating the branches in theselocations, effective reduction of darkened areas caused by misalignmentof the branches and pixel electrode edge portions can be achieved.

FIG. 7 shows a portion of an MVA LCD according to yet a furtherembodiment. Compared with the MVA LCD illustrated in FIGS. 1 to 6, theLCD shown in FIG. 7 is provided with a plurality of slit patterns 340arranged in arrays and is able to achieve the desired viewing anglewithout provision of protrusions on the color filter substrate. As shownin FIG. 7, the pixel electrode 320 has a generally cross-shaped mainbody 390 a and a plurality of projections 320 b formed by extension ofthe generally cross-shaped main body 320 a. In the LCD shown in FIG. 7,each pixel includes four domains, A, B, C, and D, wherein theorientation of the liquid crystal molecules are set to four differentdirections in order to effectively improve the LCD viewing angleperformance.

Each pixel area is also provided with a storage capacitance electrode350, which has a cross-shaped central part 350 a and two side parts 350b. The cross-shaped central part 350 a is formed generally at a locationthat is opposite the cross-shaped main body 320 a of the pixel electrode320. The two side parts 350 b are connected to each other via thecross-shaped central part 350 a and are placed separately in the pixelarea at a location adjacent the data lines 108. Compared with thestorage capacitance electrode in the conventional LCDs that generallyhas only the transverse portion of the above-mentioned cross-shapedcentral part 350, the storage capacitance electrode 350 has two sideparts 350 b and a central part 350 a that includes both transverse andvertical portions to provide an additional storage capacitance. Thecapacitance electrode 350 is created along with the gate line 106 andgate electrode of the TFT, by patterning a gate metal layer. Thecapacitance electrode 350 and gate line 106 are shown in FIG. 7 as agray pattern. As the gate metal layer is formed by electricallyconductive but opaque metal, such as aluminum, chromium, tantalum, ormolybdenum, the vertical portion of the central part 350 a and two sideparts 150 b of the capacitance electrode 350 can be used as an auxiliarylight shielding layer to shield from any leaked light.

The multi-step driving technique can also be used with the FIG. 7embodiment to achieve reduced disclination of liquid crystal molecules.

In the LCDs shown in FIGS. 1 to 6, a plurality of protrusions arearranged in arrays on the color filter substrate and a plurality of slitpatterns arranged in arrays at the pixel electrode on the TFT substrate.Alternatively, such arrangements can be swapped such that slit patternsare provided at the common electrode of the color filter substrate andprotrusions are provided on the TFT substrate. Alternatively, bothprotrusions and slit patterns can be provided on each of the colorfilter substrate and TFT substrate (e.g. protrusions provided on boththe color filter substrate and TFT substrate, and slit patterns providedon both the color filter substrate and TFT substrate).

The process used to form said protrusions is described below. To formthe protrusions on the color filter substrate, first the surface of thecolor filter substrate is coated with photoresist and a predefinedpattern is provided (refer to protrusion shown in FIGS. 1 to 6). Thenthe patterned photoresist is developed into protrusions. Next, the slitpatterns are formed along with the pixel electrodes.

While the invention has been disclosed with respect to a limited numberof embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover such modifications and variations as fall within the truespirit and scope of the invention.

1. A liquid crystal display comprising: first and second substrates; aliquid crystal layer between the first and second substrates; aplurality of gate lines and data lines provided on the second substrate,wherein the gate lines and data lines are arranged to form a pluralityof pixel areas arranged in a matrix; a plurality of pixel electrodesprovided in the pixel areas; first structures formed on the firstsubstrate; and second structures formed on the second substrate, thefirst and second structures to regulate orientation of the liquidcrystal layer so that when a voltage is applied, liquid crystalmolecules of the liquid crystal layer are aligned in predeterminedoblique directions; wherein a gap between the first and secondstructures is greater than or equal to 30 μm, wherein the secondstructures include a plurality of slit patterns that are provided at thepixel electrodes and each of the slit patterns is provided with aplurality of jagged notches, wherein the first structures include aplurality of protrusions provided on the first substrate; wherein: eachof the protrusions is provided with a plurality of branches, thebranches being provided opposite respective edge portions of a pixelelectrode; each of the pixel electrodes is divided by the slit patternsinto a plurality of partial electrodes, and neighboring partialelectrodes being connected by at least one connector joint.
 2. Theliquid crystal display of claim 1, wherein the first and secondstructures are generally parallel to each other and are arranged in analternating arrangement.
 3. The liquid crystal display of claim 1,wherein the liquid crystal layer includes liquid crystal molecules thatare generally perpendicular to a main surface of the first substratewhen no substantial electric field is applied to the liquid crystallayer.
 4. The liquid crystal display of claim 1, comprising amulti-domain vertical alignment liquid crystal display.
 5. The liquidcrystal display of claim 1, wherein each connector joint has a firstpart and a second part, wherein the first part extends generallyperpendicularly to the protrusions, and the second part extendsgenerally parallel to the data lines, and wherein the second part ofeach connector joint completely overlaps the branch of an adjacentprotrusion.
 6. A liquid crystal display comprising: first and secondsubstrates; a liquid crystal layer between the first and secondsubstrates; a plurality of gate lines and data lines provided on thesecond substrate, wherein the gate lines and data lines are arranged toform a plurality of pixel areas arranged in a matrix; a plurality ofpixel electrodes provided in the pixel areas; first structures formed onthe first substrate; second structures formed on the second substrate,the first and second structures to regulate orientation of the liquidcrystal layer so that when a voltage is applied, liquid crystalmolecules of the liquid crystal layer are aligned in predeterminedoblique directions; wherein a gap between the first and secondstructures is greater than or equal to 30 μm, wherein one of the firststructures and the second structures include a plurality of slitpatterns and each of the slit patterns is provided with a plurality ofjagged notches; and a plurality of storage capacitance electrodes thatare separately provided in the corresponding pixel areas, each storagecapacitance electrode being generally H-shaped and having a central partand two side parts, the two side parts being connected to each other viasaid central part; wherein each pair of a capacitance electrode and apixel electrode form a storage capacitance unit. each connector jointhas a first part and a second part, wherein the first part extends 7.The liquid crystal display of claim 6, wherein the first structuresinclude a plurality of protrusions provided on the first substrate, andthe second structures include a plurality of slit patterns that areprovided at the pixel electrodes.
 8. The liquid crystal display of claim6, wherein the first structures include a plurality of slit patternsprovided on the first substrate, and the second structures include aplurality of protrusions provided on the second substrate.
 9. The liquidcrystal display of claim 6, wherein the first structures include aplurality of slit patterns provided on the first substrate, and thesecond structures include a plurality of slit patterns provided at thepixel electrodes.
 10. The liquid crystal display of claim 7, wherein:each of the protrusions is provided with a plurality of branches, thebranches being provided opposite respective edge portions of a pixelelectrode; each of the pixel electrodes is divided by the slit patternsinto a plurality of partial electrodes, and neighboring partialelectrodes being connected by at least one connector joint.